This invention relates to a semiconductor integrated circuit device with high resistance against external electrostatic noise.
With semiconductor integrated circuit devices, damage due to electrostatic noise applied through package terminals is a serious problem. For this reason, protective circuits of various types have been considered. FIG. 5 is a pattern diagram of a prior art protective circuit of a commonly used kind. In FIG. 5, numeral 51 indicates an electrode pad for receiving a signal, numeral 52 indicates a protective resistor comprising polysilicon in a conductive layer above a semiconductor substrate (not shown) and numeral 53 indicates a protective transistor. The received signal is introduced into an internal circuit through a conductive polysilicon line 54. An equivalent circuit of this protective circuit is shown in FIG. 6.
In a real large scale integrated circuit, however, it is hardly avoidable that the polysilicon line 54 cross another signal line (such as a metallic layer) 55 as shown in FIG. 5 because there are many signal lines near the electrode pad 51. In FIG. 5, numeral 56 indicates the area at which the polysilicon line 54 and the signal line 55 cross each other. Sectionally, this crossing area 56 looks as shown in FIG. 7 wherein numeral 57 indicates an insulative film.
When an electrostatic noise is applied to the electrode pad 51, it is attenuated at the contact part of the polysilicon line 54 with the internal circuit because of the protective resistor 52 and transistor 53 but it is not possible to completely remove the electrostatic noise from the polysilicon line 54 and it is particularly difficult if the resistance of the protective resistor is small. If a strong electric field is induced at the crossing area 56 between the polysilicon line 54 and another signal line 55, there is an increased possibility of electrostatic damage at such an area.